来自《耶鲁大学开放课程：基础物理 第4集 第4集》

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  So I pull it by various amounts and I study the spring.
  我把弹簧拉伸不同的长度来研究这个弹簧
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  And I've learned, by studying the spring, that the force it exerts
  通过研究弹簧得知它产生的力
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  is some number k, called a force constant,
  就是某个量 k 即弹性系数
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  times the amount by which I pull it.
  乘以我拉伸的长度
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  If I start off the mass in a position
  如果物体的起点位置处
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  where the spring is neither expanded nor contracted,
  弹簧既没有拉伸也没有压缩
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  that's what we like to call x = 0.
  我们把这个位置称为 x = 0
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  So I pulled it to x = A.
  我把物体拉到了 x = A
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  Now, what I'm told is
  我所知道的是
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  when you pull it to any point x,
  物体被拉到任何一点 x 时
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  that's the force the spring exerts.
  这就是弹簧产生的力
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  So, this is part of an independent study.
  这是属于一项独立的研究